Capillary electrophoresis as a versatile tool for analysis of kinetics, functions, and structures of metal and...

Capillary electrophoresis (CE) is a crucial separation technique for charged analytes, ranging from small ions to macromolecules. Beyond separation, CE serves as a powerful tool for elucidating the kinetic, functional, and structural properties of metal and biomolecular complexes. This review highlights three key aspects of CE. First, the capillary electrophoretic reactor (CER) is introduced as a novel method to estimate dissociation rate constants of metal and biomolecular complexes. The unique reaction environment of CE enables continuous removal of complex components, facilitating dissociation. Application of CER to deferasirox metal complexes, used in iron-overload treatment, underscores the importance of dissociation kinetics in pharmacokinetics. Expanding the CER time domain from 10³ s to 10⁰-10⁵ s was achieved using microchip CE and ligand substitution reactions. Additionally, CER applications to biomolecular complexes, including DNA-protein and enzyme-inhibitor, are discussed. Second, affinity CE (ACE) is applied to functional analysis of carbonic anhydrase (CA). Binding studies of native and metal-substituted CA to a sulfonamide inhibitor highlight the critical role of amide nitrogen preorganization in the tetrahedral coordination of Zn^II and Co^II supported by three histidine residues (His₃) in apo-CA. ACE also reveals exceptionally strong Zn^II retention by His₃. Third, CE enables solution-state characterization of probe complexes, including positional isomers of hetero-trilanthanide-thiacalix[4]arene complex and inclusion complex of cis/trans-bis(o-iminobenzosemiquinonato)platinum(II) with β-cyclodextrins. These findings establish CE as a transformative technology for kinetic stability evaluation, functional analysis, and structural characterization, with broad implications across inorganic chemistry, biology, and biomedicine.